Fibrous structure of the joint capsule in the human shoulder

The fibrous structure and arrangement of joint capsules of human shoulders [8 males (7 right, 6 left), 4 females (4 right, 3 left)] were observed under a low magnification microscope as well as a polarized microscope on film preparations (Häutchen-Präparat, Vogt 1935) with reference to stained sections (mainly with H, E and orcein). The joint capsule is composed of synovial and fibrous layers and is classified into three types according to tissue composition [areolar (loose connective tissue-Fawcett, 1986) type, fibrous (dense fibrous- Fawcett, 1986) type and adipose type- (Key 1932)]. In the joint capsule of the shoulder, the areolar type was found in the anterior region, and the fibrous type in the posterior, superior and inferior regions; the adipose type was not found. The author found that the fibrous layer of the fibrous type basically has a 3 layered structure; the composition and arrangement of fibers differ depending on the type of layer. These three layers were named in order from the synovial layer as "Internal fibrous layer (IFL)", "Intermediate fibrous layer (MFL)" and "External fibrous layer (EFL)". The external fibrous layer can normally be directly visualized by peeling off the muscles. The EFL consists of external fascia, tendons and their transitional regions, which compose the joint of the shoulder. IFL and MFL can only be observed under a low magnification microscope and are distinguishable on film preparations. The IFL, which is located immediately under the stratum synoviale, consists of fibrous bundles approximately 20 microns thick. The MFL, which is adjacent to the IFL, consists of 100-400 microns thick fibrous bundles. The IFL and the MFL have a differently fixed arrangement. The fibrous bundle of EFL is slightly thicker than that of IFL and the arrangement of the fibrous bundle is like that of supraspinatus m., infraspinatus m. and teres minor m. in the superior and posterior regions of the joint capsule. The local existence as well as the arrangement of the fibrous layer of these three different types is discussed from the standpoint of mechanical movement of the shoulder joint.